The invention relates to a debarking mechanism for the excortication or pretreatment of trees for separately performed final barking and for the expulsion of at least some of the removed barks from a wood flow passing through the debarking mechanism, said debarking mechanism comprising a number of rotatable debarking shafts extending parallel to the advancing direction of the trees to be fed therethrough, which are provided with a number of teeth extending beyond the circumferential surface of the shaft and adapted to strip bark off the presently processed trees transversely to the lengthwise direction of the trees and at the same time to convey the trees transversely relative to said shafts, and said shafts, together with the teeth thereof being adapted to constitute at least a section of a support surface, upon which the presently processed trees travel through the debarking mechanism, and said shafts being adapted to each other in such a way that the processed trees perform a circular motion in the debarking mechanism, in which motion the trees are forced upon the support surface constituted by the debarking shafts, by the action of their rotatory motion, in their turn into the upper position, from which they roll down to the lower position above the other trees being processed in the debarking mechanism.
This type of prior known debarking mechanisms are provided with finger plates between the uppermost debarking shaft and the side wall of the debarking mechanism—in some mechanisms also between the debarking shafts—to prevent trees from getting wedged between the debarking shaft and the side wall of the debarking mechanism or between two debarking shafts and thus to prevent the wedged tree from getting broken.
The barks can usually get out from between the debarking shaft and the fingerplate or between two debarking shafts. The barks getting off the trees in long strips, instead, cause problems by stuffing the gaps between the uppermost debarking shaft and the related fingerplates, thus causing the barks to gather into big lumps at these uppermost finger plates.
In order to eliminate these disadvantages, the debarking mechanism of the invention has been arranged in such a way, that the uppermost debarking shaft has been provided with a guiding surface, said guiding surface together with the uppermost debarking shaft forming a slot converging in the rotational direction of the debarking shaft. The mentioned guiding surface, on one hand, helps the barks to get into the said slot and, on the other hand, prevents the trees from getting into the slot between the guiding surface and the uppermost debarking shaft.
The guiding surface is preferably provided with grooves in order to arrange said guiding surface and the teeth of the uppermost debarking shaft interlocked.
A freely rotating roller or a roller rotated by a suitable driving apparatus has proved to be the most efficient form of application of the guiding surface.
In yet another preferable application of the invention, the higher the debarking shaft lies, the bigger the selected circumferential speed of the debarking shaft is. This arrangement, on one hand, prevents the trees from getting wedged between the debarking shafts and, on the other hand, causes the barks to get out from the debarking mechanism easier.
At least one of the debarking shafts, most preferably the uppermost debarking shaft, has been moved sideways towards the inner part of the debarking mechanism in such a way that the said debarking shaft makes the trees conveyed by the lower debarking shaft to change their direction of motion so that when dividing the motion into a horizontal and a vertical component, the horizontal component of motion points towards the inner part of the debarking mechanism.
The new position of the uppermost debarking shaft causes that the trees, at the best, cannot at all go over the uppermost debarking shaft, nor can the trees, as a result of the above, hinder the barks from going into the slot between the uppermost debarking shaft and the said guiding surface.